Expert Comment: Tour de FranceWednesday 3 July 2013
As the Tour de France enters its fifth day, Hope's Dr Simon Marwood and Marc Wells look at the effect of power variation on cycling performance.
Following three days on the island of Corsica, on Tuesday the Tour de France rolled on to mainland France for the team time-trial, a 25km dash through Nice, starting and finishing on the sea front. Though a number of riders were dropped in the mountains of Corsica and lost time on the rest, because the first three stages were either neutralised or finished in a bunch sprint, nearly half the field were within just 1 second of the leader, who managed to “gap” the rest during the sprint to the finish on Sunday. Because of this, before Tuesday’s team time-trial (where the 9 riders of a team ride in formation, taking 4 – 5 second turns at the front whilst their team-mates shelter behind them) all but one of the teams had at least one rider just one second away from the lead and the coveted Yellow Jersey (Maillot Jaune). The team time-trial was bound to open up gaps in the field and so the new wearer of the Yellow Jersey would come from the winning team.
As it turned out, the racing in the team time-trial was incredibly close, with Orica-GreenEdge shading Omega-Pharma-Quickstep by just 0.75s, leaving Australian Simon Gerrans in the Yellow Jersey. Our research into cycle time-trial performance is focused on the effect of power variation on cycling performance.
One aspect of this is computer modelling of the mechanical effect of power variation on performance, and we have shown that varying power around a given sustainable mean power results in impaired performance during a flat time-trial ('Effects of magnitude and frequency of variations in external power output on simulated cycling time-trial performance', Marc Wells, Greg Atkinson & Simon Marwood, Journal of Sports Sciences 2013, epublication ahead of print).
The average speed of the winning team was nearly 58 km / hour, which we can estimate as being equivalent to an average power output of the lead rider of approximately 700 – 750 W, depending on the exact values of aerodynamic drag. Using computer modelling, our calculations show that if the team completed the first half of the race at a higher power output than the second half, the amount of variation above and below to the average power need only be 8 – 9% before the 0.75s winning margin is accounted.
It is therefore feasible that one component of the winning performance was not superior fitness of Orica-GreenEdge, but superior pacing strategy and the ability to sustain a constant speed throughout the time-trial. Optimising your pacing strategy to save less than a second may seem to some a “marginal gain”, but try telling that to Simon Gerrans, Orica-GreenEdge and Omega-Pharma-Quickstep.
Picture: Tour de France - London 2007. Photo by jtlondon. http://www.flickr.com/photos/34607608@N00/771393055/in/photolist-2baAhg-2bc9uA-2y5VmP-3hkfVS-4GhyG2-56GY8B-59h3Gc-5tatTY-5HZyuK-5SgbcU-6Dgj5P-6DgjAZ-6EkW1z-6Emkb8-6EmMVc-6EnMTa-6EodwV-6EovQB-6EpWS3-6Eq3s4-6Eq3Zh-6EqcJW-6Eqj8o-6Eqy3d-6EqQyi-6EqSd1-6EqZPG-6ErnRe-6Eruyq-6ErGo9-6ErMWA-6ErNxg-6ErRxD-6ErSfE-6ErXQc-6Es3ro-6Es4Mc-6Escbv-6Eshz6-6EsJE8-6EsWbe-6Et17w-6Et3RF-6EtbSH-6Eu51r-6Euxav-6EuM6q-6EveYU-6EvkhW-6Evtta-6EvE7s Licensed under CC BY-ND